This section is from the book "Philadelphia Cook Book: A Manual Of Home Economies", by Sarah Tyson Heston Rorer. Also available from Amazon: Philadelphia Cook Book.
Frying, though one of the most common of the culinary operations, is one that is least commonly performed perfectly well. It often results in burning the outside, while the inside is cold, or serving the article in a coating of grease. It is very important, that the oil, lard, or dripping should be very hot (about 3600 Fahr.) before the article is put in. We cannot insist too strongly on this point. There should be sufficient fat to immerse the article to be fried. If too many things are put in the fat at one time they will be badly fried, because the temperature of the fat will quickly fall below the point necessary to fry properly. The most successful frying is when the temperature rises four or five degrees during the frying. The temperature of the fat should vary according to the nature of the things fried. To ascertain when it is of the proper heat without a thermometer, throw in a little bit of bread, if it browns quickly the fat is ready; if it burns the bread, it is too hot. Fish, potatoes, croquettes and rissoles, require the fat quite hot, say about 3850 Fahr., doughnuts, crullers and fritters 300o to 320o Fahr.
A wire frying-basket is very convenient for frying croquettes, potatoes, etc.
 
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